The present invention relates to integrated circuits, and more particularly to a programmable soft-start control for a charge pump in a semiconductor-integrated circuit.
Flash memory cards have a range of voltage requirements in order to drive the integral flash-memory devices, controllers, and analog circuits. A charge pump is a typical power-supply circuit that is capable of providing for these voltage requirements through voltage conversion.
In systems that use flash memory cards, as such a card is hot-plugged, it is desirable to extend the time period to fully power the card in order to control the high inrush or surge current at turn on. If the current is not controlled, damage may be done to the card's connectors and components. Additionally, the power supply circuit breaker may also trip resulting in a shutdown of the whole system. Accordingly, a soft-start is performed by controlling the ramp-up rate of the applied voltage(s) in order to provide a relatively constant current to the card's load capacitance while it is charging. Inrush current limiting is also beneficial because dv/dt control reduces both the EMI due to current and voltage spikes, and the stress on capacitors and the semiconductor devices surrounding the circuitry.
For flash memory cards, embedded charge pumps provide several amps to an array of flash memory devices and typically control the voltage ramp-up rate with a timing capacitor. However, because these circuits use timing capacitors, such circuits lack the ability to adjust for finer soft-start control and the ability to quickly program specific soft-start settings according to desired pump turn-on conditions.
Therefore, there is a need for a programmable soft-start control in a charge pump circuit that allows for finer soft-start control via firmware and that adds flexibility to applying specific soft-start settings according to charge pump turn-on conditions.